1. Field of the Invention
This invention generally relates to an ignition coil. This invention particularly relates to an ignition coil which can be fitted into a plug hole in each cylinder of an internal combustion engine.
2. Description of the Related Art
A typical ignition coil has a housing, a coil portion, and a connector portion. The housing is cylindrical. The coil portion is provided in the housing. The coil portion includes a central core, a primary winding, a primary spool, a secondary winding, and a secondary spool. The primary winding is provided on the primary spool. The secondary winding is provided on the secondary spool. The primary spool and the secondary spool are located coaxially around the central core. The primary spool extends outward of the secondary spool. The primary spool, the secondary spool, and the central core are spaced from each other. Spaces in the housing are occupied by epoxy resin which fixes the parts to each other, and which provides insulation thereamong. During the manufacture of the typical ignition coil, casting epoxy resin is injected into the housing. The connector portion is provided on an upper part of the housing. The connector portion has a locating member. A ring-shaped locating rib extends downward from a lower end surface of the locating member. Voids tend to remain in the epoxy resin after the manufacture of the typical ignition coil. The voids decrease the fixing and insulating performances of the epoxy resin.
U.S. Pat. No. 5,949,319 corresponding to Japanese patent application publication number P2000-501895A discloses a bar coil for use as an ignition coil which is designed as follows. Casting resin can be introduced into an interior space of the bar coil. The bar coil has a centrally arranged channel that extends from a connecting segment, through a core of the bar coil, and to a pan-shaped bottom area of the interior space of the bar coil. During the manufacture of the bar coil, casting resin flowing through the channel enters the closed bottom area, from which it is diverted as a uniform front to flow through gaps in the bar coil to the connecting segment. Specifically, casting resin is introduced directly into the bar coil, downstream of the windings, through a channel which is longer than each of the windings of the bar coil. The casting resin travels from the channel into gaps that are adjacent to the windings. Thus, the bar coil can be filled rapidly, and the casting resin rises as an essentially uniform front back in the opposite direction through the gaps. This prevents air inclusions which would shorten the insulating clearance after curing as bubbles in the casting resin and could thus lead to failure of the bar coil.
It is an object of this invention to provide an improved ignition coil.
A first aspect of this invention provides an ignition coil comprising a housing; a central core portion located in the housing; an inner spool disposed in the housing and located outward of the central core portion; a first winding provided on the inner spool; an outer spool disposed in the housing and located outward of the inner spool; a second winding provided on the outer spool; a locating member including a locating rib positioned adjacent to an upper portion of the central core portion, the locating rib being provided in a gap between the inner spool and the central core portion and locating the inner spool and the central core portion relative to each other; insulating resin injected into the housing and providing insulation among parts in the housing; wherein at least one of the inner spool and the locating member has a void-escape passage which connects the gap and an outside of the inner spool with each other, and which allows a void to escape from the injected insulating resin in the gap.
A second aspect of this invention is based on the first aspect thereof, and provides an ignition coil wherein the void-escape passage includes a spool-side void-escape hole formed in the inner spool and extending between an inner circumferential surface and an outer circumferential surface of the inner spool.
A third aspect of this invention is based on the first aspect thereof, and provides an ignition coil wherein the void-escape passage includes a spool-side void-escape slit formed in the inner spool and extending between an inner circumferential surface and an outer circumferential surface of the inner spool, the spool-side void-escape slit opening at a top surface of the inner spool.
A fourth aspect of this invention is based on the first aspect thereof, and provides an ignition coil wherein the void-escape passage includes a locating-member-side void-escape hole formed in the locating member and extending through a wall of the locating member at a place inward of the locating rib, the locating-member-side void-escape hole connecting the gap and an outside of the housing.
A fifth aspect of this invention is based on the first aspect thereof, and provides an ignition coil wherein the void-escape passage is formed in the inner spool, and the locating rib has an auxiliary void-escape passage extending between an inner circumferential surface and an outer circumferential surface thereof and communicating with the void-escape passage.
A sixth aspect of this invention is based on the first aspect thereof, and provides an ignition coil wherein the central core portion has a resilient member at its upper end.
A seventh aspect of this invention is based on the first aspect thereof, and provides an ignition coil wherein the void-escape passage includes a spool-side void-escape recess formed in the inner spool.
An eighth aspect of this invention is based on the seventh aspect thereof, and provides an ignition coil wherein the spool-side void-escape recess is formed in an inner circumferential surface of the inner spool.
A ninth aspect of this invention is based on the seventh aspect thereof, and provides an ignition coil wherein the spool-side void-escape recess is formed in an upper end surface of the inner spool.
A tenth aspect of this invention is based on the first aspect thereof, and provides an ignition coil wherein the void-escape passage includes a locating-member-side void-escape recess formed in the locating member.
An eleventh aspect of this invention is based on the tenth aspect thereof, and provides an ignition coil wherein the locating-member-side void-escape recess is formed in an outer circumferential surface of the locating rib.
A twelfth aspect of this invention is based on the tenth aspect thereof, and provides an ignition coil wherein the locating-member-side void-escape recess is near a base of the locating rib.
A thirteenth aspect of this invention is based on the first aspect thereof, and provides an ignition coil wherein the void-escape passage includes a void-escape rib hole formed in the locating rib and extending between an inner circumferential surface and an outer circumferential surface of the locating rib.
A fourteenth aspect of this invention is based on the thirteenth aspect thereof, and provides an ignition coil wherein the locating rib fits into a groove in the locating member.
A fifteenth aspect of this invention is based on the fourteenth aspect thereof, and provides an ignition coil wherein the void-escape rib hole is located at a place where the locating rib fits into the groove in the locating member.
A sixteenth aspect of this invention is based on the thirteenth aspect thereof, and provides an ignition coil wherein the void-escape rib hole communicates with a hole extending through a wall of the locating member.
A seventeenth aspect of this invention is based on the first aspect thereof, and provides an ignition coil wherein an upper end of the central core portion has a small-diameter part, and the locating rib fits around the small-diameter part, and wherein the void-escape passage includes a wide gap defined between an outer circumferential surface of the locating rib and an inner circumferential surface of the inner spool.